As shown in the website, 120 LEDs may be controlled with just 17 wires, connected to pins set to OUTPUT.

I get how we can control at least one diode of the pairs below, but what happens when we want to turn on the full board? Is that possible? More specifically, how could we turn on adjacent LEDs in order to form a square, for example?

I hope that the question is not too dumb.

120 LEDs

  • \$\begingroup\$ Actually, the number of wires can be reduced further: Just use 8 rows and 8 columns, keeping the antiparallel LED arrangement the same, and you have 64 x 2 = 128 LEDs controlled by just 16 wires. \$\endgroup\$ – Anindo Ghosh Oct 31 '13 at 7:15
  • \$\begingroup\$ You can turn on multiple diodes by asserting multiple lines. But you certainly can't show all possible combinations. E.g. you can't have 3 of the 4 corners of a rectangle lit. \$\endgroup\$ – MSalters Oct 31 '13 at 10:31

Not a dumb question, just inexperienced. We turn on multiple LEDs one or a group at a time, and then rely on persistence of vision to fill in the rest. This is the same mechanism that a television or monitor uses to display an entire screen; it scans one line at a time, and PoV causes us to "see" the whole image at once.

  • \$\begingroup\$ Basically, I just turn on and off faster than the eye may perceive the change? \$\endgroup\$ – Cehhΐro Oct 31 '13 at 4:39
  • \$\begingroup\$ @Fiire: That is exactly it. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 31 '13 at 4:39

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